Hi Nati -- thanks for the feedback.
1. We do plan to support searching for tasks in the future
2. We currently show the how many checklist items are completed on the card -- are you specifically interested in the checklist case (as a percentage) or are you interested in percent complete more generically?
3. We've heard this feedback from some other users as well and we're evaluating some ideas here. For now, we usually hear people use labels to represent priorities and filter as needed.